Native fluorescence of extravasated proteins. A new method for quantitation of macromolecular vascular leakage

Macromolecular vascular leakage into rat tracheal lumen is quantified by a new method that does not require the administration of an exogenous macromolecular tracer or dye to the animals. The magnitude of vascular leakage is determined by the concentration of extravasated plasma proteins measured by their native fluorescence and assayed against diluted plasma. Native fluorescence of proteins (PNF), when excited at 295 nm and measured at 340 nm, is almost exclusively due to tryptophan fluorescence. The PNF assay can be used in the range of protein concentration of 0.1-120 micrograms/mL. The results obtained in the PNF assay were found to be equivalent to the results from two other conventional assays where fluorescent or radioactive albumin was used as the external macromolecular tracer.